Technology has been established for many mammals such as cattle, whereby fertilized eggs are obtained by in vitro fertilization, embryos are developed from fertilized eggs by in vitro culture, the thus obtained embryos are implanted into the uteri of recipient females for conception, and thus progeny are obtained.
However, embryos obtained by in vitro culture are problematic due to low conception rates. For example, the conception rates of cattle range from 40% to 50%. Human pregnancy success rates range from about 25% to 35%. Possible reasons therefor are poor development and the like, since in vitro culture environments differ from in vivo environments.
Development of techniques for selecting embryos having high conception rates based on morphology or biochemical indicators have been attempted.
Non-patent document 1 discloses that in human fertilized eggs, conception rates differ depending on the number of cells and fragmentation at the time of third cleavage.
Non-patent document 2 discloses that in human fertilized eggs, the conception rates are improved when there are few instances of fragmentation.
Non-patent documents 3 and 4 describe that in bovine fertilized eggs, when the number of cells at the time of third cleavage is not 5 to 8 cells, chromosome aberration takes place particularly easily.
Non-patent document 5 describes that in bovine fertilized eggs, conception rates fluctuate depending on respiratory volume (the amount of oxygen consumed), and a respiratory volume of 0.78-1.10 nl/h leads to the highest conception rate.
Non-patent document 6 describes the examination of the relationship between combinations of a plurality of indicators (e.g., the number of cells at the time of initial cleavage, the time required for initial cleavage to take place, the uniformity of 2-cell embryos at the time of initial cleavage, the number of cells at the time of second cleavage, amino acid level, and the like in porcine fertilized eggs) and blastocyst (%).
Patent document 1 discloses an invention relating to a method for evaluating embryo quality. The document describes that unsynchronized cell division at the time of cleavage and fragmentation phenomenon can be used as indicators for quality evaluation. The document further describes that these indicators may be combined with other indicators such as respiration rate.
Patent document 2 discloses an apparatus and a method for measuring the amount of oxygen consumed per single embryo in order to evaluate embryo quality.
The relationship between each individual indicator and embryo quality has been examined as described above. However, no prior art exists in which the relationship between a combination of a plurality of indicators and conception rate is specifically examined.
Furthermore, in the case of cattle, even the relationship between an individual indicator and conception rate has almost never been examined under current circumstances.
Meanwhile, fertilized eggs of a non-human mammal are generally cultured by a method that involves placing droplets of a culture solution in wells on a culture vessel, coating the surfaces of the microdroplets with mineral oil, and then placing a plurality of fertilized eggs within one droplet (droplet method). This method is problematic in terms of differential management of individual embryos. Hence, embryo quality is determined using as an indicator only the morphological observation for embryos at the completion of culture (the early blastocyst stage, the blastocyst stage, or the expanded blastocyst stage). Conventional methods for culturing embryos are problematic in terms of obtaining indicators for selecting embryos having high conception rates by following embryonic growth process over time from the initial cleavage to the completion of culture so as to obtain data, and then combining data at different time points. Such a method of obtaining indicators has never been examined conventionally.